1. Field of the Invention
This invention relates to distributing frames for wiring interconnection.
2. Related Art
Conventional Distributing Frames, or DF's, are typically a cross-hatch of vertical and horizontal planes, so that outside cable pairs terminated on the vertical side may be interconnected to central office equipment cable pairs, terminated on the horizontal side. Interconnection of outside terminal pairs and equipment terminal pairs is effected by means of two-wire cords known as cross-connections, or jumpers. Vertical planes provide a means for cross-connections to move vertically, and horizontal planes, or shelves, provide a means for cross-connections to move horizontally.
FIG. 1 illustrates a small conventional linear distributing frame, consisting of 10 verticals (V1 through V10) and 3 shelves (S1 through S3). Each vertical has a termination capacity of 30 outside cable pairs, and each shelf has a termination capacity of 100 equipment cable pairs. In FIG. 1, numbers of shelves, verticals, and individual terminals have been limited to small amounts so that interconnection principles can be more easily illustrated. The actual number of shelves on a conventional DF typically ranges from 12 to 16, and the number of verticals from 100 to 500 or more. Termination capacities of verticals on conventional DF's typically range from 600 to 800; termination capacity of conventional shelves typically ranges from 40 to 60 pairs per opposing vertical.
In the distributing frame of FIG. 1, an outside wire cable 1 travels from the central office cable vault, through a slot 2, continuing on one face (called the cable face) of vertical V3, where it is terminated on an outside wire connector block 3. The number of terminals on the connector block 3 match the number of pairs contained in the outside cable. These terminals project through to the other face of the vertical plane, called the cross-connect side or face. An individual terminal pair 4 on the connector 3, is shown being cross-connected via a two-wire cord 5 which travels down the cross-connect face of vertical V3, through a ring 6, located at the intersection of vertical V3 and shelf S2, horizontally along the top face of shelf S2, and terminating on an individual terminal pair 7, located on equipment connector block 8. The terminals on the horizontal connector block likewise project through the block to the lower face of the shelf, where they are connected to a pair of wires in a central office equipment cable 9. This cable 9 travels on the lower face of the shelf S2, up the cable face of vertical V8, and onto an overhead cable rack 10, leading to the switch or other equipment.
FIG. 2 illustrates the final state of a vertical and a shelf of the DF shown in FIG. 1, wherein an ideal or perfect distribution of equipment was made to outside cable pairs. All individual outside cable terminals 4 on vertical V are connected to equipment terminals located on shelves physically closest to them. All cross-connections 5, therefore, pass through the closest ring 6. Upon entering the shelf S, these cross-connections are connected to the physically closest individual equipment terminals 7.
In FIG. 2, the density of cross-connections in all cross-sections would be measured as zero, since no cross-connections pass through any of them. Also, the lengths of all cross-connections made, in terms of the number of cross-sections traveled, would be zero.
In theory, equipment growth would be matched perfectly with outside cable requirements and growth, resulting in the ideal distribution state depicted in FIG. 2. In reality, however, this ideal final distribution state will rarely, if ever, exist. This is partly because the initial distribution state is typically as shown in FIG. 3. In FIG. 3, some initial multiple cross-connections are made on the DF shown in FIG. 1. A total of seven cross-connections 5 travel from their respective individual outside cable pair terminals 4, on any vertical V, through their respective rings 6, and onto various shelves. On any shelf S, a total of 4 cross-connections 5, travel from their respective rings 6, and terminate on various individual equipment pair terminals 7. Densities 17 of cross-connections in vertical cross-sections 15 are shown as counts of cross-connections passing through them. Densities 18 of cross-connections in horizontal cross-sections 16 are likewise shown as counts of cross-connections passing through them.
Historically, every effort was made to keep the state of the distribution as close as possible to the ideal state shown in FIG. 2. Maintaining a close to ideal state may be possible on a small scale, but as a DF grows to larger dimensions and frame activity (disconnects and connects) increases, the chances of this happening become smaller. The question of what the predictable final distribution state of a DF will be is significant to DF design because densities and lengths of cross-connections at ultimate capacity depend on this. The lack of an accurate prediction of a final distribution state has hampered many prior re-design efforts.
FIG. 4 illustrates the final state of vertical V and shelf S when the distribution is perfectly random. In FIG. 4, ten cross-connections emanate from every vertical terminal group 11, and are equally dispersed to each of the rings 6. This is indicated by each of the lines 12, each containing 3 and 1/3 cross-connections. Densities 17 in each of the vertical cross-sections 15 are shown. Each ring 6, in turn, receives 3 and 1/3 cross-connections from each vertical terminal group 11, for a total of 10 cross-connections passing through each ring 6, and traveling onto each shelf. On any shelf S, all rings 6 disperse all 10 cross-connections 13 equally to all 10 horizontal terminal groups 14. Thus, each line 13 on shelf S represents a single cross-connection. Densities 18 in each of the horizontal cross-sections 16 are shown.
In reality, the final state of the DF shown in FIG. 1 would not be exactly as shown in FIG. 4. For one reason, fractional cross-connections do not exist. For another, real randomness is seldom, if ever, perfect. However, the perfectly random final state does represent an analyzable situation. It also most accurately represents the statistical probability statement that all outside cable pairs have an equal probability of being connected to any equipment cable pair. Since a primary goal of any central office design was to match and coordinate, as closely as possible, equipment expansion with outside cable expansion, and implement a cable assignment process which would produce a distribution as close to the ideal as possible, the perfect random state may be regarded as an accurate upper limit of the randomness of the final state of the frame.
Some of the prior art attempts at reducing interconnection lengths and densities have failed because their designs were based on the assumption that the randomness of matching outside cable pair to inside cable pair was primarily limited to randomly matching pairs of one outside cable to pairs of one inside cable.
Using the perfect random final state as an upper limit, the following can be proved for the conventionally designed horizontal growth distributing frame:
1. The average cross-connection length on either a vertical or a horizontal plane is one-third the length of that plane. Total average length, therefore, is one-third the length of the vertical plane plus one-third the length of the horizontal plane. On a conventional DF, the vertical plane length remains constant while the horizontal length grows. The final average length, therefore, is very accurately approximated as one-third the length of the horizontal plane. On some existing DF's, this is as much as 150 feet or more. PA1 2. The maximum cross-connection length is the full length of the vertical plane plus the full length of the horizontal plane. Since horizontal plane length is much greater than vertical plane length, the maximum cross-connection length is accurately approximated as simply the length of the horizontal plane. PA1 3. Density variation on both the vertical and horizontal planes is parabolic, having a maximum at the mid-point, and a minimum at the extremities. This is not much of a problem on the conventional vertical plane, since it never increases in length, and hanging wires do not tangle as easily as a pile resting on a shelf. However, on long shelves, the density buildup at the mid-point can have catastrophic effects, causing DF abandonment and re-termination to another frame. The cost of this is easily in the millions of dollars. PA1 1. Closing the horizontal planes on themselves, thereby eliminating a mid-point. PA1 2. Using vertical growth to a height which balances distances traveled horizontally.
The limitations inherent in conventional DF design have led, in many cases, to the creation of intermediate DFs, or IDFs. These IDFs must be connected to the main DF (MDF) containing outside cable pair terminations, and to each other. This is accomplished by a system of tie cables inside the central office building. As more outside cable pairs enter a central office building, IDFs and associated tie cables proliferate. Proliferation of IDFs wastes floor space that could be used for switches or other central office equipment. Further, proliferation of tie cables wastes duct and rack space that could be used for outside wire riser cables and interior equipment cable. The overall effect, especially in large metropolitan areas, where high rise buildings are common, is that the volume of space available within a building is under-utilized, causing less $/cubic foot to be earned than is ultimately possible.